Knickpoint Migration: Processes, Rates, and Form

长期以来，临界点迁移一直被认为是河流对基准面突然下降做出反应的主要机制。由于基准面下降可由构造剧变、气候变化、海平面下降或河流捕获引发，因此在广泛的地质、构造和气候环境中，关键点迁移是航道切割和景观演变的一个重要方面。在基准面突然下降之后，在分水岭内活跃迁移的临界点的分布在已经调整到新的基准面的地貌和那些没有调整到新的基准面的地貌之间设定了边界，因此保留了它们残留的切割前的形态。因此，随着构造或气候条件的变化，景观响应的时间尺度和泥沙向盆地输送的时间受到上游临界点迁移速度和类型的强烈影响。尽管临界点在景观演变中至关重要，但对临界点迁移速率和类型的控制知之甚少。我们打算在新西兰北岛东开普省的怀保阿流域进行一项自然的实验，在那里进行了18ka的摆设迁徙。一百多个灯笼划定了沿着怀保阿干流开始的一波切割的向前推进，大约18ka，正如废弃阶地冲积填土中的Tephra地层学所记录的那样。初步的地图和航空摄影调查表明，在流域内，临界点的迁移率和形式(扩散的、陡峭的/离散的、瀑布的)都表现出相当大的变异性。将收集、分析和传播与上游流域面积(流量和泥沙通量)、基质岩性和临界点迁移距离有关的临界点迁移的过程、速率和方式的重要新数据。由于怀保阿是一个戏剧性的例子，说明我们生活的环境是多么充满活力，它多么容易受到人类干扰的影响，我们致力于开发各级教育模块，包括K-12教学。

Knickpoint migration has long been recognized as a primary mechanism of river response to sudden base-level fall. As base-level fall can be triggered by tectonic upheaval, climatic change, sea-level fall or river capture, knickpoint migration is an important aspect of channel incision and landscape evolution in a wide range of geological, tectonic, and climatic settings. Following a sudden base-level fall, the distribution of actively migrating knickpoints within a watershed sets the boundary between landforms that have adjusted to the new base level and those that have not, and therefore retain their relict, pre-incision form. Consequently, the time scale of landscape response and the timing of sediment deliver to basins following a change in tectonic or climatic conditions is strong influenced by the rate and style of upstream knickpoint migration.Despite the critical importance of knickpoints in landscape evolution, little is known quantitatively about the controls on the rates and styles of knickpoint migration. We propose to exploit a natural experiment in knickpoint migration that has been running for 18 ka in the Waipaoa drainage basin on the East Cape of New Zealand's North Island. Over on hundred knickpoints demarcate the headward advance of a wave of incision initiated along the Waipaoa trunk stream at about 18ka, as recorded in tephra stratigraphy in alluvial fills on abandoned strath terraces. Preliminary map and aerial photography investigation indicates that both knickpoint migration rate and form (diffuse, steep/discrete, waterfall) show considerable variability within the drainage basin. Significant new data on the processes, rates, and styles of knickpoint migration as a function of upstream drainage area (discharge and sediment flux), substrate lithology, and distance of knickpoint migration will be gathered, analyzed, and disseminated. As the Waipaoa is a dramatic example of how dynamic the landscape we live in is, and how susceptible it can be to human disturbance, we are committed to the development of educational modules at all levels, including K-12 instruction.